Current limiting vacuum fuse



April 5, 1966 R. H. ALRlGHT CURRENT LIMITING VACUUM FUSE Filed Fa. e, 1964 2 Sheets-Sheet 1 N Nv R. H. ALBRIGHT 3,244,839

CURRENT LIMITING VACUUM FUSE April 5, 1966 2 Sheets-Sheet 2 Filed Feb. 6, 1964 W Ra wf Ti f mw w W4 4 y n a f R, W

United States Patent O 3,244,839 CURRENT LIMITING VACUUM FUSE Roy H. Albright, Greensburg, Pa., assignor to I-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Filed Feb. 6, 1964Ser. No. 342,935 8 Claims. (Cl. 20D- 120) The instant invention relates to protective means for circuits of high current capacity and more particularlyto a current limiting fuse having a fuse element in a vacuumized chamber for use in protecting electrical circuits having potentials of 600 volts or greater.

Current limiting fuses find widespread use in the protection of current carrying circuits. The normal function of these fusesV is to have their fuse elements blow or melt away under predetermined conditions of current magnitude so as to prevent currents of greater thanthe critical magnitude to reach the circuit being protected by the fuse elements and thereby severely damage or destroy thecomponents of such a circuit. In high voltage applications, Le., in applications where the circuit has ratings of 600 volts, or greater, it is normalto employ a current limiting fuse which has the characteristics of severely limiting the let-through current passing through the fuse simultaneously with the interruption operation performedby the fuse. Such current limiting fuses are normally designed to have long fusible elements (i.e., wires) wound on a ceramic core in a helicalfashion and surroundedv byl sand such as, for example, silver sand. which provides the function of absorbing the energy emitted by the fuse element as and when it blows. The fuse elements are necessarily of limited cross-sectional area softha't melting begins in a relatively short time, preferably during the rst major current-increase due to faulted current conditions. The use of long fuse elements of limited cross-sectional areas places some restrictions on fuse designs, particularly in higher current ratings as the heating under normal current conditions becomes prohibitive.

In addition to the above conditions, high transient overvoltages are caused by the fuse interruptions. The magnitudes of these over-voltages are a function of the letthrough current, as well as the cross-section area and total length of the fusible element.

The above disadvantages of present current-limiting fuses are overcome by the fuse of the instant invention which is designed to provide adequate current limiting and fuse blowing characteristics with a relatively short fusible element. For a given currentrating the fusible element can be further reduced in cross-sectional areaft'o attainy desiredl time-current characteristics. Large conductors adjacent tothe fuse elements considerably reduce heating under normal currentv conditions thereby permitting fuses to be designed for higher current ratings than presently available fuses. These improvements in fusible elements tend to reduce let-through currents during fuse operation with subsequent reduction in magnitude of transient over-voltages.

The fuse assembly of the instant invention isf comprised of a fuse housing containing rst and secondl rodshaped electrodes mounted' to the ends of the-fusehousing by fuse end caps. Substantially the entire length of each rod-shaped electrode projects into the interior of the fuseV housing and the gap between the opposing faces ofthe rod-shaped elements is very small. The gap is bridged by a fuse element being necessarily of an extremely short length which is electrically connected-to the opposing-'faces of. the' rod-shaped electrodes. The entire chamber housingthe rod-shaped electrodes andthe fuse element is completely vacuumized so as to provide` extremely good dielectric characteristics for the fuseassembly when the fuse element has blown.

The use of a very short fusible element between electrodes of extremely high thermal capacity thereby permits a much reduced size of fuse element for any given current rating. This arrangement substantially reduces the value of let-through current on fuse interruption. In addition thereto, the transient over-voltage is appreciably reduced due to the lower value of let-through current and the extremely short length of the fuse element. In addition thereto, the extremely short fuse elements permits substantially lower temperature rises during the interruption operation as compared with present day current limiting fuses. In addition thereto, exposure of substantially all of the surfaceY area of the rod-shaped electrodes to the vacuum chamber provides marked improvement over present day fuses due to the fact that when a fuse element has interrupted the encasement of the remaining parts in the vacuum continues to provide high dielectric characteristics over the entire internal length from ferrule to ferrule.

As an alternative embodiment to that described above, the fuse assembly may be modified by placing an insulating member in the fuse assembly so as to surround the gap between the rod-like electrodes which is bridged by the fusibleV element. The insulating member is provided for the purpose of housing the fusible element and also for receiving sand such as, for example, silver sand, which completely surrounds the fusible element and acts to absorb the large amount of heat given olf by the fusing of the element; The insulating member may be formed of a porous materiall so as to enable the region within its interior to be vacuumized together with the vacuumizing of the entire fuse assembly chamber. This arrangement has the advantage over theprevious embodiment described in that it provides a sand for absorbing the great heat energy generated by theI fusible element during the blowing thereof while at the same time retaining the vacuum chamber characteristics of the former embodiment. The porous insulating member may be transparent to permit visual observation of the interior thereof in order to ascertain whether the interior chamber has been appropriately filled with the' sandv as wellr as permitting a visual 0bservation for determining whether or not the fuse has blown;

A still further alternative embodiment which is designed for the purpose of -providing'a suitable supporting strength for the fusible element is comprised of rod-shaped electrodes of the type previouslydescribed with their opposing faces eachl being provided with a cylindrical cavity. An insulating rod bridging the gap between the rod-shaped electrodes is` inserted into each of the cavities and secured thereto by a suitable adhesive material. The region surrounding the insulating rodis thenpacked-with sand which is. then surrounded and coniine'dby a cylindrical-shaped fusible element securedl adjacent the outer periphery ofthe rod-shaped electrode opposing faces. The exterior of the cylindrical-shaped fusible element is also surrounded byfsand` and in turn surrounded by'a porous transparent tubular member which acts to contain' the sand inthe region surrounding the fusible element. The entire interior chamber ofi the fuse assembly is vacuumized in the same' manner as previously described with the transparent porous tubular member enabling the region containing the sandto likewise'be vacuumizedk As. a still further embodiment, the fusible element surrounded-by sand may be prepared as aseparate cartridge comprised of a tubular transparent porous member housing'rst and second'electrodes positioned at opposite'ends thereof` with: the fusibleI element bridging the opposing faces of the electrodes. The entire interior region surroundedby theV porous tubular member is suitably filled withsand. The cartridge may then be inserted in any of the-three embodiments described abovewith the electrodesprovided therein being secured in any suitable manner to the huge rod-shaped electrodes provided in the fuse assembly. This arrangement provides substantially simplified handling of the fuse assembly during the construction thereof.

It is therefore one object of the instant invention to provide a fuse assembly for use in current-carrying circuits with the fuse assembly -being so designed as to provide relatively small over-Voltage and let-through currents as well as generating substantially reduced amounts of heat under normal operating conditions as well as when the fuse blows as compared with the substantially higher characteristics of such prior art devices.

Another object of the instant invention is to provide fuse assemblies in high voltage circuits having `current carrying capacities considerably in excess of present current limiting fuses by using extremely large rod-shaped electrodes having an extremely small gap therebetween, which gap is bridged by an extremely short fusible element and contained in a vacuum chamber. l ,y Another .object of the instant invention is'to provide fuse assemblies with extremely large rod-shaped electrodes having an extremely. small gap therebetween, which gap is bridged by an extremely short fusible element with the entire fuse assembly interior being confined in a vacuum chamber'having high dielectric characteristics.

Still another object of the instant invention is to provide a novel fuse assembly for use in circuits wherein the fuse assembly is comprised of a vacuum chamber containing rst and second elongated rod-shaped electrodes having an extremely small gap therebetween wherein Vthe gap is bridged by an extremely short fusible element and further having sand surrounding the fusible element, which sand is held in place by a porous tubular insulating member to maintain the sand firmly surrounding the fusible element so as to absorb heat from the fusible element during the blowing of the fuse.

Still another object of the instant invention is to provide a novel fuse cartridge for use in fuse assemblies having a vacuum chamber containing rst and second elongated rod-shaped electrodes having an extremely small gap therebetween wherein the cartridge designedtherefore is comprised of an extremely short fusible element secured at opposite ends thereof to first and second electrodes and which is surrounded by sand held rmly into place by a transparent porous tubular member such that the cartridge may readily be inserted to bridge the gap between the opposing faces of the rod-shaped elec'- trodes.

, Still another object of the instant invention is to provide a novel fuse assembly for use in circuits wherein the fuse assembly interior chamber is comprised of first and second rod-shaped electrodes having their opposing faces secured to one another by an insulating rod and further being bridged by an extremely short fusible element which in turn is surrounded by sand provided for the purpose of absorbing the heat generated by the fusible element when the fuse blows.

These and other objects of the instant invention will become apparent when reading the accompanying description and drawings in which:

. FIGURE 1 is a cross-sectional view of a fuse assembly designed in accordance with the principles of the instant invention.

FIGURE 2 is a cross-sectional view of an alternative embodiment of the fuse assembly of FIGURE 1'.

FIGURE 3 is a cross-sectional View of still another alternative embodiment for the fuse assembly of FIG- URE 1. i

FIGURE 4 is a cross-sectional view of a fuse cartridge which may be employed in the fuse assemblies of FIGURES 1-3.

FIGURE 1 shows a first preferred embodiment 10 of the instant invention which is a fuse assembly comprised of a transparent insulated elongated tubular mem-v Cil ber 11 having first and second end caps or ferrules 12 and 13 respectively, each of which are secured to the tubu lar insulating member 11 and having their skirts 12a and 13a respectively, secured to the transparent member by the adhesive means 14 which may, for example, be cement. Each of the end caps 12 and 13 are provided with openings 12b and 13b respectively, and having rigidly secured and electrically connected thereto the elongated rod-shaped electrodes 15 and 16 respectively. As can be seen from the figure the rod-shaped electrodes 15 and 16 are formed of a solid metallic material of extremely good conductivity and further that the rodshaped members have relatively huge dimensions.

The rod-shaped members 15 and 16 are so positioned as to provide an extremely small gap 17 separating their opposing faces 15a and 16a. A fuse element 18 bridges gap 17 and is rigidly secured to faces 15a and 16a in any suitable manner so as to provide a current pathfor the fuse assembly extending from end cap 12 through rod 15, fuse element 18, rod 16 and endfcap 13. It should be understood that the fuse assembly 10 may be mounted and supported by fuse clips [not shown] which are normally used-in present day fuse installations.

,The interior chamber 19 of fuse assembly 10, which is confined by the transparent tubular member 11 and the end caps 12-13 and rod-shaped members 15-16, is completely vacuumized so as to provide extremely good dielectric characteristics. This arrangement is employed to provide extremely high breakdown voltage characteristics so that when the fuse element 18 blows there will be no arcing between the electrode rods 15 and 16 [which may, for example, be formed ofcopperL The use of such huge electrode rods provides extremely high current carrying capacities for the fuse assembly which also have extremely high thermal capacity characteristics. The extremely short length of the fuse element provides the advantageous characteristics of generating extremely low over-voltage conditions and an extremely small amount of heat as well as extremely small let-through currents for the fuse assembly as compared with fuse assemblies of present day devices.

FIGURE 2 shows an alternative embodiment 10 for the fuse assembly 10 of FIGURE 2 wherein like elements are designated with like numerals. The electrode rods 15 and 16 of FIGURE 2 differ from the rods 15 and 16 of FIGURE 1 in that they are each provided with a shoulder or notch 15b' and 1Gb', which notches act as a means for receiving the fusible element 18 which is secured thereto. The narrow gap 17 and the slightly wider gap 17' are completely housed by a porous transparent tubular member 21. The region 20 within tubular member 21 is packed with sand such as, for example, silver sand, in such a manner that the sand in region 20 completely surrounds fusible element 18. The interior chamber 19 is vacuumized in the same manner as the embodiment of FIGURE 1 and the tubular member 21 is made vporous so as to insure the fact that the entire region occupied by the sand 20 is also vacuumized to the same extent as the vacuumized chamber 19.

Tubular members 14 and 21 are made transparent in order to permit visual observation of the interior region surrounded by the tubular members so as to observe whether the interior region 20 has been packed with sand. In addition thereto, the tubular transparent members permit observation of the interior region in order to ascertain whether or not the fusible element has blown. The amount of sand provided is suiiicient to absorb the heat generated by the fusible element 18 and this amount is markedly less thanthe amount of sand employed in present day fuse assemblies due to the fact that in such assemblies such as, for example, the fuse assembly covered in U.S. Patent 3,012,121, issued December 5, 1961, and assigned to the assignee of the lnstantinvention, it will be found in this patent that sand is required in an amount sulicient to cover and surround au extremely helically wound fusible element since the only protection vwhich the sand provides is that of absorbing heat emitted from the fusible element as it blows. This protection is fully afforded in the embodiment of FIGURE 2 of the instant application while at the same time requiring substantially less sand for performing this function as compared with the amount of sand required in the fuse assembly of the above mentioned U.S. patent.

FIGURE 3 shows still another alternative embodiment wherein like elements as between FIGURES 1 and 3 are designated by like numerals. The embodiment 10 differs from that of FIGURE 1 in that the rod electrodes and 16" are each provided with a cylindrical cavityv 15a" and 16a respectively, which cavities receive a cylindrically-shaped insulating rod 22. The rod 22 is secured in the cavities 15a" and 16a by a suitable adhesive 23 such as, for example, cement. In the embodiment of FIGURE 3, first and second fusible elements 18 and 18 bridge the gap 17 between the opposing faces of the electrode rods 15" and 16". This entire region is confined by a porous tubular transparent member 21 substantially identical Vto the one shown in FIGURE 2. The transparent member acts to confine the sand introduced into the interior region in such a manner as to completely surround insulating rod 22 and fusible elements 18 and 18. Tubular element 21 is again made porous to insure the fact that the interior region surrounded by tubular member 21 will be vacuumized at the same vtime that the interior chamber 19 of the fuse assembly 10" is vacuumized. The structure 10" of FIG- URE 3 affords advantages over the two previous embodiments in that by tying electrode rods 15 and 16 together in a secure manner such as is shown in FIGURE 3, Vthis greatly facilitates the ease of handling of the electrode assembly as well as the positioning and assembly of this electrode assembly into the overall fuse assembly. While embodiment 10" provides for the use of multiple fuse elements, it should be understood that the embodiments 10 and 10 of FIGURES l and 2 respectively, may likewise be .provided with such multiple fuse elements.

In order to further provide ease of handling and assembly of the vacuumzed fuse of the instant invention it is possible to employ a fuse cartridge such as, for example, the fuse cartridge shown in FIGURE 4 which is comprised of a transparent porous tubular member 21 having secured at opposite ends thereto rod-shaped electrode members 31 and 32. The opposing faces 31a and 32a of these electrodes have secured thereto a fusible element 18. The entire interior region confined by the tubular member 21 is completely filled with sand 20. The cartridge 30 of FIGURE 4 may be employed in any of the embodiments of FIGURES 1 3 simply by securing the surfaces 31b and 32h of disc-shaped electrodes 31 and 32 respectively to the opposing faces of the electrode rods 15 and 16 provided in the interior of the fuse assembly of FIGURE 1, for example. This greatly facilitates the fabrication and assembly of the overall fuse assembly 10 by enabling the cartridge 30 to be produced first and then subsequent thereto to be very simply and readily inserted into the gap 17 of the fuse assembly 10 without any danger of harming or breaking the fusible element.

The gap provided between the copper electrode rods is a fraction of an inch gap which necessarily receives an extremely short fusible element thus insuring an extremely large decrease of the over-voltage let-through current and heat generation characteristics of the fuse assembly as compared with present day fuse assemblies. Also, by providing electrode rods of extremely huge overall dimensions and by exposing substantially all of the surface of said rods to the vacuum in the interior chamber, this provides the advantage of maintaining high dielectric characteristics over the entire internal length of the fuse.

Although there has been described a preferred embodiment of this novel invention, many variations and modifications will now be apparent to those skilled inthe art. Therefore, this `invention is to be limited, lnot by the specific disclosure herein, but only by vthe appending claims.

What is claimed is:

1. Fuse means for use in protectinghigh `voltage circuits comprising a hollow tubular member formed of insulating material; first and second Vcylindrically yshaped metallic end caps, each Vhaving skirts enclosing theopposing ends of said tubular member; Yfirst and second electrode rods each having a first end thereof rigidly secured to an associated end cap, the second ends of said rods facing one another to form a small gap therebetween; said rods having a relatively large diameter to form substantially huge rigid rod members; each of -said rods being slightly less thanhalf the length of said fusemeans to form a small gap; va fusible element bridging said gap and being electrically connected Yto the second ends of said rods; the length of said fusible element being substantially the length of said gap; the region enclosed by said tubular member and said end caps forming a chamber which is vacuumized to provide a vhigh dielectric characteristic in the region of said fusible element, second tubular insulating means bridging said gap and surrounding the second ends of `said rod members and said fusible element; the region defined by said gap and said second tubular insulating means containing sand completely `surrounding said fusible element.

'2. Fuse means for use in protecting high voltage circuits comprising a ,hollow tubular member formed of insulating material; first and second cylindrically shaped metallic end caps, each having skirts enclosing the opposing ends of said tubular member; first and second electrode rods each having a first end thereof rigidly secured to an associated end cap, the second ends of said rods facing one another to form a small gap therebetween; said `rods having a relatively large diameter to form substantially huge rigid rod members; each of said rods being Slightly less. than half the length of said kfuse means to form a small gap; a fusible element bridging said gap and being electrically connected to the second ends of said rods; the length of said fusible element being substantially the length of said gap; the region enclosed by said tubular member and said end caps forming a chamber which is vacuumized to provide a high dielectric characteristic in the region of said fusible element, second tubular insulating means bridging said gap and surrounding the second ends of said rod members and said fusible element; the region defined by said gap and said second tubular insulating means containing sand completely surrounding said fusible element, said second tubular member being porous to enable said gap region tov be in the vacuumized condition.

3. Fuse means for use in protecting high voltage circuits comprising a hollow tubular member formed of insulating material; first and second cylindrically shaped metallic end caps, each having skirts enclosing the opposing ends of said tubular member; first and second electrode rods each having a first end thereof rigidly secured to an associated end cap, the second ends of said rods facing one another to form a small gap therebetween; said rods having a relatively large diameter to form substantially huge rigid rod members; each of said rods being slightly les-s than half the length of said fuse means to form a small gap; a fusiblerelement bridging said gap and being electrically connected to the second ends of said rods; the length of said fusible element being substantially the length of said gap; the region enclosed by said tubular member and said end caps forming a chamber which is vacuumized to provide a high dielectric characteristic in the region of said fusible element, second tubular insulating means bridging said gap and surrounding said fusible element; said gap region containing sand completely surrounding said fusible element; said rod second ends each being formed to provide a ledge for securing said fusible element to said rods.

4. Fuse means for use in protecting high voltage circuits comprising a hollow tubular member formed of insulating material; first and second cylindrically shaped metallic end caps, each having skirts enclosing the opposing ends of said tubular member; first and second electrode rods each having a first end thereof rigidly secured to an associated end cap, the second ends of said rods facing one another to form a small gap therebetween; said rods having a relatively large diameter to form substantially huge rigid rod members; each of said rods being slightly less than half the length of said fuse means to form a small gap; a fusible element bridging said gap and being electrically connected to the second ends of said rods; the length of said fusible element being substantially the length of said gap; the region enclosed by said tubular member and said end caps forming a chamber which is vacuumized to provide a high dielectric characteristic in the region of said fusible element, second tubular insulating means bridging said gap and surrounding said fusible element; said gap region containing sand completely surrounding said fusible element; said rod second ends each having an annular cavity; tubular reinforcing means having its ends inserted into said cavities; adhesive means securing said tubular reinforcing means to said rods; said fusible element bridging said gap and being secured to said rods near the periphery thereof.

5. Fuse means for use in protecting high voltage circuits comprising a hollow tubular member formed of in sulating material;

first and second cylindrically-shaped metallic end caps, each having skirts enclosing the opposing ends of said tubular member;

first and second electrode rods each having a first end thereof rigidly secured to an associated end cap, the second ends of said rods facing one another to form a small gap therebetween; v

said rods having a relatively large diameter to form substantially huge rigid rod members;

each of said rods being slightly less than half the length of said fuse means to form a small gap therebetween;

a fuse cartridge means positionable between the oppos# ing faces of said rods and within said small gap being comprised of a tubular insulating member;

first and second disc-shaped electrodes inserted into opposite ends of said tubular member;

a fusible element secured to the opposing faces of said discshaped members in the interior of said cartridge means;

:said interior being packed with sand;

said first and second electrode rods each having an opening for receiving one associated end of said fuse cartridge means wherein the disc-shaped electrodes make electrical engagement with said first and second rods within said openings.

6. The device of claim 5 wherein said tubular insulating member of said cartridge means is a transparent porous member.

7. The device of claim 6 wherein said gap is a fraction of an inch;

the length of said fusible element being a fraction of an inch.

8. The device of claim 7 wherein the diameter of said fusible element is many times smaller than the diameter of said rods.

References Cited by the Examiner UNITED STATES PATENTS 897,852 9/1908 Sachs 200-120 1,687,246 10/1928 Hickey 20G-131 2,625,626 1/1953 Matthysse 200-120 2,665,348 1/ 1954 Kozacka 200--120 2,777,033 1/ 1957 Kozacka 20G-120 2,939,934 6/1960 Kozacka 200-120 FOREIGN PATENTS 599,748 l/ 1926 France.

508,078 6/ 1939 Great Britain.

BERNARD A. GILHEANY, Primary Examiner.

H. B. GILSON, Assistant Examiner. 

1. FUSE MEANS FOR USE IN PROTECTING HIGH VOLTAGE CIRCUITS COMPRISING A HOLLOW TUBULAR MEMBER FORMED OF INSULATING MATERIAL; FIRST AND SECOND CYLINDRICALLY SHAPED METALLIC END CAPS, EACH HAVING SKIRTS ENCLOSING THE OPPOSING ENDS OF SAID TUBULAR MEMBER; FIRST AND SECOND ELECTRODE RODS EACH HAVING A FIRST END THEREOF RIGIDLY SECURED TO AN ASSOCIATED END CAP, THE SECOND ENDS OF SAID RODS FACING ONE ANOTHER TO FORM A SMALL GAP THEREBETWEEN; SAID RODS HAVING A RELATIVELY LARGE DIAMETER TO FORM SUBSTANTIALLY HUGE RIGID ROD MEMBERS; EACH OF SAID RODS BEING SLIGHTLY LESS THAN HALF THE LENGTH OF SAID FUSE MEANS TO FORM A SMALL GAP; A FUSIBLE ELEMENT BRIDGING SAID GAP AND BEING ELECTRICALLY CONNECTED TO THE SECOND ENDS OF SAID RODS; THE LENGTH OF SAID FUSIBLE ELEMENT BEING SUBSTANTIALLY THE LENGTH OF SAID GAP; THE REGION ENCLOSED BY SAID TUBULAR MEMBER AND SAID END CAPS FORMING A CHAMBER WHICH IS VACUUMIZED TO PROVIDE, A HIGH DIELECTRIC CHARACTERISTIC IN THE REGION OF SAID FUSIBLE ELEMENT, SECOND TUBULAR INSULATING MEANS BRIDGING SAID GAP AND SURROUNDING THE SECOND ENDS OF SAID ROD MEMBERS AND SAID FUSIBLE ELEMENT; THE REGION DEFINED BY SAID GAP AND SAID SECOND TUBULAR INSULATING MEANS CONTAINING SAND COMPLETELY SURROUNDING SAID FUSIBLE ELEMENT. 